Improvements In Or Relating To Well Abandonment

ABSTRACT

An apparatus and method for anchoring a string at a well for the purpose of cutting a tubular ( 30 ) which includes an anchor mechanism ( 110 ) being a tubular body ( 60 ) having a cone ( 116 ) arranged around the body, a plurality of selectively operable slips ( 112 ), and a plurality of pistons ( 44 ), there being a piston for each slip, each piston being operable to act to move each slip independently over the cone between a retracted configuration and an extended configuration wherein the outer surface ( 96 ) of each of the slips contacts the inner surface of the tubular ( 30 ). The method includes the action of cutting the tubular ( 30 ) with a cutting tool ( 102 ) which is stabilised by the slips ( 112 ).

The present invention relates in particular to apparatus for removing asection of tubular such as casing or lining from a well, and relatedmethods.

In the oil and gas exploration and production industry, tubulars such asrisers, casing or lining are used to carry fluids and equipment fromdeep underground to topside facilities for the processing ofhydrocarbons. In subsea wells, it is typical to have a number ofconcentrically arranged casings, each of which extends progressivelydeeper in the well and upon which further casing/liner strings aresuspended to reach the desired depth. Typically, the first casingsection is a 30″ (762 mm) conductor which is cemented into the seabed.This conductor can extend from the seabed, typically through a rigstructure to the topside facilities. Progressively smaller diametercasings e.g. 20″ (508 mm), 13⅜″ (340 mm), 9⅝″ (244 mm) are inserted andsupported from casing hangers. A 7″ (178 mm) liner may then be suspendedat the extremity of the innermost casing. Cement or grout is located inthe annulus between concentric casings to stabilise the wellbore wall,for example by preventing collapse of formation material into thewellbore, and can help to control pressure and provide fluid containmentin the wellbore during use of the wellbore, such as when drilling orproducing oil or gas.

In various situations it can be desirable to remove a section of thetubing which has previously been installed at a well. Typically, thisinvolves cutting the casing to produce a cut section of a manageablesize, and then pulling on the cut section to remove it. Removal ofcasing or lining may be a necessary and important part of a plug andabandonment operation for abandoning a well, where there may typicallybe a need to remove the casing in order to provide a suitable plug forthe well. For complete abandonment of a well, UK legislation requiresthe removal of the wellhead together with all casing to a depth of 3 mbelow the seabed.

Previous approaches to removing sections of casing or lining in awellbore have involved running a cutting tool and a pulling tool intothe wellbore in separate trips for performing the cutting and pullingoperations respectively. By performing these operations in separatetrips however, such approaches can be inefficient and costly.Accordingly, combined casing cutting and pulling tools have beendeveloped so that the cutting and pulling of the casing can be achievedon a single trip. Such a tool is the TRIDENT® System to the presentApplicants, Ardyne Technologies Limited.

WO2017046613 describes a cutting and pulling tool which advantageouslyhas a cutting tool which can be operated by rotation of the work stringwhile the pulling tool is anchored to the inside wall of the casingsection above the cut to hold the casing in tension and providestability to the cutting action. The pulling tool may be considered asan anchor or spear.

A prior art anchor mechanism for assisting in the cutting operation and,if required, for pulling the tubular is illustrated in FIGS. 1A and 1B.The present invention is an improvement on this design. For completenessin understanding this invention, the prior art anchor mechanism of FIGS.1A and 1B will be reviewed to provide a framework to understand thepresent invention.

FIG. 1A is a sectional view of an anchor mechanism 10 in a run-inconfiguration. The principle of operation of the anchor mechanism 10 isto force slips 12 up a slope or ramp 14 of a cone 16 so that the slips12 move outwards and engage the tubular 30. The slips 12 are movedaxially by a piston in the form of a sleeve 18 actuated by a hydraulicforce being the fluid pressure against a face 20 of the sleeve 18. Thesleeve 18 acts against a spring 22. The slips 12 are retained by anunderside 24 of the sleeve 18. On pumping fluid through the central bore26, by virtue of a restriction arranged in the bore below the anchor(not shown), fluid enters ports 28 to act against face 20. Sleeve 18moves axially acting on the slips 12 forcing them up the ramp 14 of thecone 16. The slips 12 move radially outwards until their travel islimited by the underside 24 of the sleeve 18. As the slips 12 traveloutwards they will engage the inner surface 32 of the tubular 30. Thisis as illustrated in FIG. 1B.

In this example, the slips 12 engage 9⅝″ (244 mm) tubular 30. To set theslips into the surface 32 of the tubular 30 an over pull would typicallybe applied which forces the cone 16 under the slips 12 to drive themfurther outwards to anchor onto the tubular 30. Such action means thatthe fluid through the bore 26 can be stopped or varied withoutactivating or de-activating the slips 12. When the anchor mechanismrequires to be unset, weight is set down on the mechanism 10, so as tomove the cone 16 away from the slips 12, the release of support coupledwith the bias on the spring 22 releases the slips 12 from contact on theinner surface 32 of the tubular 30. The slips 12 are drawn back and theanchor mechanism can be moved and reset elsewhere.

In the mechanism 10, a single piston in the form of the sleeve 18 actsagainst the slips 12 to move them uniformly radially outwards. Thus eachslip travels at the same rate over the same distance. It is assumed thatthe mechanism 10 is on a central axis of the tubular 30 and the innersurface 32 is circular in cross-section. In this way, the slips 12 willall touch the inside surface 32 at the same time and grip to the samedegree, thus maintaining the centralised position of the mechanism 10when anchored which should centralise the cutting tool.

A disadvantage of this mechanism 10 exists when the inner surface is notcylindrical. As the tubular 30 has been in use for the life of the well,the inner surface may have become corroded or have deposits from scaleor other debris. Further due to compression, the tubular 30 may havebuckled and now provide a non-circular cross-section. Additionally, itis known in the construction of some tubing, particularly the 30″ (762mm) conductor, to roll and weld plate which creates a longitudinal seamweld on the inner surface 32. FIG. 1C shows the effect of the mechanism10 being set in a tubular 30 where a seam weld 34 causes a discontinuityon the inner surface 32. In the prior art, when the sleeve 18 acts onthe slips 12, if a slip 12 a meets the weld 34, then the mechanism 10 ismoved off axis as the slip 12 a continues to expand radially outwardsuntil the opposing slip 12 c contacts the inner surface 32. Continuedexpansion, causes effective gripping by only two slips 12 a, c andsetting of the mechanism 10 and tool string off-axis. Besides reducingstability, the blades on the cutting tool may not cut through the entiretubular 30 at the weld 34 preventing pulling of the tubular or thelifting capacity of the spear could be severely compromised aspotentially only a proportion of the slips would be load bearing. FIG.1C shows the effect with four slips 12 a-d, but the effects will beapparent with any number of slips.

It is therefore an object of the present invention to provide apparatusfor anchoring a string at a well for the purpose of cutting a tubularwhich obviates or mitigates at least some of the disadvantages of theprior art.

It is a further object of the present invention to provide a method foranchoring a string at a well and cutting a tubular which obviates ormitigates at least some of the disadvantages of the prior art.

According to a first aspect of the present invention there is providedapparatus for anchoring a string at a well for the purpose of cutting atubular, including an anchor mechanism, the anchor mechanism comprising:

a tubular body having a central bore between an inlet and a firstoutlet, the inlet and first outlet being adapted for connection in adrill string to be run into the tubular;

a cone arranged around the tubular body, the cone having an outersurface including a slope;

a plurality of selectively operable slips, each slip having an outersurface configured to grip an inner surface of the tubular and an innersurface matching the slope of the cone they are arranged upon; and

a plurality of pistons, there being a piston for each slip, each pistonbeing operable to act to move each slip independently over the conebetween a retracted configuration and an extended configuration whereinthe outer surface of each of the slips contacts the inner surface of thetubing.

By having each slip operable by a separate piston, the slips can movenon-uniformly over the cone so that if one slip meets an obstruction,the others can continue to move radially outwards to contact the innersurface of the tubular. In this way, the apparatus is centralised withinthe tubular when the anchor is set.

Preferably, the tubular body is rotatable relative to the cone. In thisway the tubular body is rotatable relative to the slips. Advantageouslythe apparatus can be used to stabilise the drill string while toolsbelow can be operated by rotation of the drill string. Preferably, abearing is located between a base of the cone and a ledge on the toolbody. In this way, with the slips set, the tool body and drill string towhich it is attached can be rotated within the static cone.

Preferably, each piston comprises a piston rod contained within acylinder arranged co-linearly with a central axis of the apparatus. Eachpiston rod is arranged to act on a face of each slip. The piston may bemechanically or hydraulically operated. In an embodiment, the piston ishydraulically operated by action of fluid from the central bore. Thisallows the slips to be moved remotely by pumping fluid from surfaceabove a pre-set flow rate threshold. Each piston rod may be configuredto move in response to fluid pressure acting on an end face of thepiston rod.

Preferably, each piston includes biasing means to hold each slip in theretracted configuration. In an embodiment, the biasing means is a springarranged in the cylinder to act against the piston rod. Advantageously,the flow rate threshold may be set by changing the spring force actingon the piston rod. This allows other tools on the string to be activatedby fluid pressure in the central bore also.

Preferably a first end of each slip is located under a lip of aconnector to each piston rod. In this way, the radial travel of eachslip is limited so that each slip is retained within the apparatus.

In an embodiment, each piston includes an emergency release arrangementso as to ensure retraction of each slip when the apparatus is moved backfrom the extended configuration to the retracted configuration.Preferably the arrangement comprises a release piston configured to acton the piston rod. A release piston rod may be attached to the pistonrod so as to move therewith, the release piston rod having an end faceof smaller surface area than that of the end face of the piston rod.Each release piston may be mechanically or hydraulically operated. In anembodiment, the release piston is hydraulically operated by action offluid from the central bore. A port may be arranged from the centralbore to the cylinder of the release piston and fluid is diverted fromthe central bore and each piston, by a drop ball locating in a seat inthe central bore.

In an alternative embodiment, the biasing means to holds each slip inthe extended configuration. In this way, the apparatus can be used as aspear to recover a cut section of tubular. In this embodiment, a lockingarrangement is provided which holds the slips in the retractedconfiguration until sufficient fluid pressure is applied. In this way,the apparatus can be run in with the slips retracted. Preferably, thelocking arrangement is resettable. Preferably, the locking arrangementis re-set by movement of the release piston. More preferably, thelocking arrangement comprises a detent in the form of a collet.

In an embodiment, the apparatus includes a plurality of selectivelyoperable centralisation pads, each pad having an outer surfaceconfigured to match an inner surface of the tubular and an inner surfacematching the slope of the cone they are arranged upon; and

the plurality of pistons including a piston for each centralisation pad,each piston associated with a centralisation pad being operable to moveeach centralisation pad independently over the cone between a retractedconfiguration and an extended configuration wherein the outer surface ofeach of the centralisation pads is at drift to the inner surface of thetubular.

Preferably the slope of the cone at each centralisation pad is steeperin gradient than the slope of the cone at each slip. In this way, thecentralisation pads are deployed ahead of the slips and thus theapparatus is centralised prior to contact of the slips with the innersurface of the tubular.

Preferably, there are an equal number of slips to centralisation pads onthe apparatus. More preferably, a centralisation pad is located betweeneach slip and spaced equidistantly around a circumference of the toolbody.

The remaining features of the pistons may be as described herein withrespect to the pistons associated with the slips.

According to a second aspect of the present invention there is provideda method for anchoring a string at a well and cutting a tubular,comprising the steps:

-   -   (a) mounting apparatus according to the first aspect on a drill        string;    -   (b) mounting a cutting tool on the drill string;    -   (c) running the drill string in the wellbore and locating the        cutting tool at a location at which the tubular is to be cut;    -   (d) setting the slips independently to anchor the apparatus to        an inner surface of the tubular to be cut;    -   (e) cutting the tubular using the cutting tool;    -   (f) unsetting the slips to release the apparatus from the inner        surface of the cut section of tubular.

In this way, by independently operating the slips, the apparatus canbetter grip the tubular regardless of any discontinuities, deposits uponor eccentricity of the tubular to which they are being anchored. This isachieved by the ability of the slips to be expanded non-uniformly fromthe apparatus.

Preferably, the method includes the step of hydraulically actuating thepistons to contact the slips to the inner surface of the tubular. Thisallows the slips to be moved remotely by pumping fluid from surfaceabove a pre-set flow rate threshold.

Preferably the method includes the step of applying an over pull to theanchor mechanism once the slips have contacted the inner surface of thetubular. This sets the anchor mechanism to prevent accidental release ofthe anchor mechanism. The tension or pulling force may wedge or lock theslips between the outer surface of the cone and the tubular or downholetubular. By setting the anchor mechanism the fluid pressure may bereduced below the pre-set threshold flow rate or stopped without theanchor mechanism being deactivated.

Preferably, the anchor mechanism is unset i.e. deactivated by applying adownward force to the tool. This force will pull the cone away from theslips and then the spring will bias the slips back into the recess.

Preferably, the slips are arranged to rotate with respect to the drillstring. In this way, the cutting tool may be operated via rotation ofthe drill string with the apparatus set against the tubular to providestability to the cutting tool.

Optionally, the method may include radially extending centralising padsindependently on the apparatus. In this way, the drill string can becentralised and with it the cutting tool before the cut is made.

Optionally, the method may include activating an emergency releasearrangement to unset the apparatus and draw the slips away from theinner surface of the tubular in the event that they don't release.

The method may include the step of removing the cut section of tubularby using the anchor mechanism as a spear.

The method may be used in tubular within the wellbore such as casing ormay be used on tubing above the wellbore i.e. in the wellhead, above theseabed and in the rig structure. The method may also find application inpipelines.

In the description that follows, the drawings are not necessarily toscale. Certain features of the invention may be shown exaggerated inscale or in somewhat schematic form, and some details of conventionalelements may not be shown in the interest of clarity and conciseness. Itis to be fully recognized that the different teachings of theembodiments discussed below may be employed separately or in anysuitable combination to produce the desired results.

Accordingly, the drawings and descriptions are to be regarded asillustrative in nature, and not as restrictive. Furthermore, theterminology and phraseology used herein is solely used for descriptivepurposes and should not be construed as limiting in scope. Language suchas “including,” “comprising,” “having,” “containing,” or “involving,”and variations thereof, is intended to be broad and encompass thesubject matter listed thereafter, equivalents, and additional subjectmatter not recited, and is not intended to exclude other additives,components, integers or steps. Likewise, the term “comprising” isconsidered synonymous with the terms “including” or “containing” forapplicable legal purposes.

All numerical values in this disclosure are understood as being modifiedby “about”. All singular forms of elements, or any other componentsdescribed herein including (without limitations) components of theapparatus are understood to include plural forms thereof.

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying drawings of which:

FIGS. 1A and 1B are longitudinal section views, and FIG. 1C is across-sectional view, of a prior art anchor mechanism in run-in and setpositions;

FIG. 2 is a longitudinal section view of an anchor mechanism in aretracted configuration according to an embodiment of the presentinvention;

FIG. 3 is a view along lines A-A′ of FIG. 2;

FIG. 4 is a longitudinal section view of the anchor mechanism of FIG. 2in an extended configuration according to a further embodiment of thepresent invention;

FIG. 5 is a longitudinal section view of the anchor mechanism of FIG. 2in an extended configuration according to an embodiment of the presentinvention;

FIG. 6 is a view along lines B-B′ of FIG. 5;

FIG. 7 is a longitudinal section view of the anchor mechanism of FIG. 2in an extended configuration according to a yet further embodiment ofthe present invention;

FIGS. 8A to 8D provide schematic illustrations of a method of removing asection of tubular from a wellbore according to an embodiment of thepresent invention;

FIG. 9 is a longitudinal section view of a portion of an anchormechanism in a retracted configuration according to a further embodimentof the present invention; and

FIG. 10 is a view along lines A-A′ of FIG. 9.

Reference is initially made to FIG. 2 of the drawings which illustratesan anchor mechanism, generally indicated by reference numeral 110,according to an embodiment of the present invention. Like parts to thoseof FIG. 1 have been given the same reference numeral with the additionof 100.

Anchor mechanism 110 is formed of a one piece cylindrical body 36,having a central bore 126 providing a through passage with a fluid inlet50 at an upper end 46 and a first fluid outlet 52 at a lower end 48. Atthe upper end 46 there is a box section 56 and at the lower end 48 thereis a pin section 58, for connecting the anchor mechanism 110 into adrill string (not shown) as is known in the art.

A difference as compared to FIG. 1A of the prior art mechanism 10 is inthe presence of a second cylindrical body 60 located around the firstcylindrical body 36. The second cylindrical body 60 has at a first end62, the cone 116 machined on an outer surface 64 thereof and at a secondend 66 a plurality of piston housings 68. A single piston housing 68 isshown in FIG. 2, but there will be a number of equidistantly spacedpiston housings 68 arranged around the cylindrical body 60. In anembodiment, there are eight piston housings 68 a-h, shown in thecross-sectional view in FIG. 3. The second cylindrical body 60 is alsoof unitary construction as for the first cylindrical body 36. An end cap70 provides closure to the piston housings 68 a-h, being attached to thesecond cylindrical body 60 by screws 72.

Each piston housing 68 is a cylindrical bore 74 containing a piston rod76. The piston rod 76 has a back plate 78 providing a back face 80. Theback plate 78 is sized to fit and move within the bore 74, while beingsealed thereto, by an o-ring 82. The piston rod 76 is stepped to providea first annular face 84 against which a spring 122 can act and a secondannular face 86 which limits the travel of the piston rod 76 from thebore 74, by contact of the face 86 with an inner wall 88 of the end 90of the housing 68. It will be noted that there is a separate spring 122in each piston housing 68 as compared to the prior art spring 22 shownin FIG. 1. Each spring 122 is biased between the first annular face 84and the inner wall 88.

The piston rod 76 is actuated in a similar manner as for the prior art,except in that a plurality of ports 128 now exist to connect the centralbore 126 to each piston housing 68 a-h. The piston rods 76 are thusdriven by fluid from the central bore acting on the back face 80.

An aperture 92 through the end 90 of the housing 68 allows the pistonrod 76 to exit the housing 68 and act upon an end face 94 of a slip 112.

In an embodiment, there are four slips 112 spaced equidistantly aroundthe cone 116 and located in box groove channels 95 as are known in theart. Each slip 112 is an elongate member having an outer surface 96 witha curvature to match that of the inner surface 32 of the tubular 30 inwhich it is intended to be set. The outer surface 96 is knurled, groovedor toothed to provide a suitable grip and bite into the inner surface 32of the tubular 30 on contact. The inner surface 98 of each slip 112 isthe reverse of the outer surface or ramp 114 of the cone 116 along thechannel 95. This is done to provide a mating arrangement.

The feature of the underside 24 of the sleeve 18 in the prior art tolimit radial travel of the slip 12, is maintained in the presentinvention. However, the underside 124 is now created by a plate 99attached to each rod 76.

An additional feature is also provided on the anchor mechanism 110.Between the base 38 of the second cylindrical body 60 and a ledge 40 onthe first cylindrical body 36 there is located a bearing 83. Bearing 83is as known in the art and allows the tubular body 36 to rotate relativeto the tubular body 60. Chevron seals 85 are also located between thebodies 36, 60 which allow rotation therebetween while maintaining a sealaround the ports 128. Thus, if the slips 112 are set, the slips 112 andthe second cylindrical body 60 can remain stationary and the firstcylindrical body 36 can rotate with the string. This allows thetransmission of rotation through the anchor mechanism 110 when theanchor mechanism 110 is set.

A yet further feature is shown on the anchor mechanism 110. An emergencyrelease system, generally indicated by reference numeral 42, is providedcomprising a secondary piston 44 located in the piston housing 68 behindand attached to the main piston rod 76. There is a release system 42 atevery piston housing 68 a-h in the anchor mechanism 110. Piston 44 has afront actuating face 54 with a smaller surface area than the backactuating face 80 of the main piston rod 76. In this way, fluid comingthrough ports 43 to the release system 42, when the same fluid pressureis delivered to ports 128 to the main piston rod 76, will cause only themain piston rod 76 to be actuated. Ports 128 are closed when theemergency release is operated via a ball landing on a ball seat 45 inthe central bore 126 between the ports 43, 128. There is no springpresent and the piston 44 is moved by fluid pressure against the frontactuating face 54 which draws the main piston rod 76 back into thehousing 68 so as to actively disengage the slips 112.

In an embodiment of the present invention a number of the slips 112 arereplaced by centralising pads 51. In a preferred embodiment, there arefour slips 112 and four centralising pads 51, with a centralising pad 51arranged between each slip 112 and spaced equidistantly around the body36. The centralising pads 51 are operated from an identical pistonhousing 68 arrangement as for the slips 112, with the exception that thepiston rod 76 now includes a stop ring 53 at face 86 to limit the travelof the piston rod 76 out of the housing 68. In this way, thecentralising pads are prevented from contacting the inner surface 32 ofthe tubular 30. The curvature on the outer surface 55 of centralisingpads 51 and the distance of travel can be made to match the curvature ofthe tubular 30 so as to drift in the tubular 30 and centralise theapparatus 110. Additionally the ramp 114 of the cone 116 can be madesteeper at the location of the centralising pads 51 as compared to theramp 114 at the slips 112 so that the centralising pads extend firstfrom the body 60. A centralising pad 51 and piston housing 68arrangement is shown in FIG. 4.

FIG. 2 illustrates the anchor mechanism 110 of the present invention ina retracted configuration. This is the run-in position. The slips 112are entirely located within the second body 60 of the anchor mechanism110, so to prevent the outer gripping surface 96 contacting any tubularon run-in. The slips 112 are at the bottom of the ramp 114 and thepiston rod 76 is held back in the piston housing 68 by virtue of thespring 122. This will be the same for all the slips 112 and centralisingpads 51, if present.

When the anchor mechanism 110 is located in tubular 30 and an anchor isrequired, the slips 112 can be set. This is achieved in an identicalmanner to the prior art anchor mechanism 10 by pumping fluid fromsurface through the central bore 126 to meet a restriction in the stringat a lower location (not shown). Fluid under pressure will then enterthe ports 128, 43. Due to the larger surface are of the back face 78,the piston rod 76 is moved towards the lower end 48, taking thesecondary piston 44 with it and compressing the spring 122. The movementof the piston rod 76 acts on slips 112 and pads 51 forcing them up theramps 114 of the cone 116. The centralising pads 51 will extend firstdue to the steeper slope of the ramp 114 at their locations but theywill also be stopped before they all can contact the tubular 30. Anycontact will move the apparatus 110 and centralise it as thecentralising pads 51 a-d take up their drift position. As the slips 112travel up the ramps 114 independently of each other, if any slip 112contacts a discontinuity on the wall of the tubular, such as a seam wellon a conductor, this slip will be prevented from moving further, but allthe other slips 112 can continue to travel outwards and will all gripthe inner surface 32 of the tubular 30. A slip 112 in the extendedconfiguration is shown in FIG. 5. The centralising pad 51 in FIG. 4 isshown in the extended configuration. Cross section through B-B′ on theseFigures is shown on FIG. 6, for the case when a discontinuity, such as aseam weld or deposit 34 is present on the wall 32 of the tubular 30.Here it is seen that the slip 112 a has not extended as far as the otherslips 112 b-d, but that the apparatus 110 remains centralised in thetubular 30, and the remaining slips 112 b-d provide firm grippingcontact with the inner surface 32 of the tubular 30, in direct contrastto the prior art case of FIG. 1C.

A majority of the slips 112 have engaged the tubular 30. To set theslips 112 into the surface 32 of the tubular 30 an over pull is appliedwhich forces the cone 116 under the slips 112 to drive them furtheroutwards to anchor onto the tubular 30. This can be considered as anextended configuration.

With the mechanism 110 now fully anchored, the fluid through the bore126 can be stopped or varied without activating or de-activating theslips 112. When the anchor mechanism requires to be unset, weight is setdown on the mechanism 110, so as to move the cone 116 away from theslips 112, the release of support coupled with the bias on the spring122 releases the slips 112 from contact on the inner surface 32 of thetubular 30. The slips 112 a-d and centralising pads 51 a-d are drawnback and the anchor mechanism 110 can be moved and reset elsewhere.

When unset, the anchor mechanism 110 returns to the retractedconfiguration, see FIG. 2. However, if the slips 112 failed to retractwhen weight was set down, the emergency release system 42 can be used. Aball 47 is dropped from surface through the central bore 126 to land inthe ball seat 45. This cuts off fluid flow to the lower ports 128 whichoperate the piston rod 76 and instead directs fluid to the secondarypiston 44. The fluid acts against the fluid actuating face 54 to movethe piston 44 back towards the upper end 46. As the pistons 44, 76 areconnected, this action draws the piston rod 76 back into the housing 68and with it the slips 112/centralising pads 51. The drop ball 47arrangement is shown in FIG. 7 with the ball 47 in place prior tomovement of the secondary piston 44. The emergency release 42 is can beoptionally included and optionally used if required.

A typical method for anchoring a string at a well and cutting a tubularusing the anchor mechanism 110, will now be described with reference toFIGS. 8A-D. Anchor mechanism 110 is mounted on a drill string 100 abovea cutting tool 102, as is known in the art. The drill string 100 is runinto tubular 30 and the blades 104 of the cutting tool located at adesired position to make a cut in the tubular 30. In the example given,the tubular is a 30′ (762 mm) conductor which may be cut either in thewellbore or above the seabed in the rig structure. If used within thewellbore the inner casing strings have been removed. As such thepresence of a packer above the anchor mechanism 110 is not required butmay be added for cutting other tubular sections. Additionally, a bridgeplug and/or drill bit to dress off a cement plug are also not requiredbut could be added to the drill string 100 if desired. For thisapplication a brush 106 and/or wiper 108 can be included on the drillstring 100, preferably below the cutting tool 102 to condition the innersurface 32 of the tubular 30 prior to anchoring and cutting. A suitablearrangement is illustrated in FIG. 8A having been run into the tubular30. During run-in the inside surface 32 of the tubular 30 will have beenwiped and cleaned of debris and other detritus which could affect thegripping action of the slips 112.

With the blades 104 located at a desired cutting position, see FIG. 8B,the anchor mechanism is set as described herein before. A restriction inthe bore of the cutting tool 102, is used to increase the pressure inthe anchor mechanism to provide movement of the piston rods 76. Eachslip 112 and centralising pad 51 will move independently, with thecentralising pads 51 come out first to centralise the string 100 andthen the slips 112 engaging the inside wall 32 of the tubular 30 unlesstheir travel is hindered by a discontinuity such as a seam weld on theconductor.

With anchor mechanism 110 set and the string 100 centralised, liftingthe string 100 can place the tubular 30 in tension in preparation forthe cut. The blades 104 can now be activated and will be stabilised byvirtue of the anchor mechanism 110 to cut through the tubular 30. Fluidcan be circulated through the cut to lubricate the blades 104 and flushmaterial out from behind the tubular 30. This is as illustrated in FIG.8C. Advantageously, the cutting tool 102 can be operated by rotation ofthe drill string 100 from surface. The drill string 100 rotates throughthe stationary anchor mechanism 110 via the bearings 83. Once the cut ismade the string 30 can be pulled again to determine if the cut has beensuccessful. In smaller size tubular cut under tension there will be anautomatic signal at surface when the cut is achieved as the tubular willpart. As the conductor has an increased weight due to its dimensions,such a signal may not be detectable. Thus it is better to check that thestring 100, with the cut tubular section attached via the anchormechanism 110, can be raised to verify the cut. By setting the anchormechanism 110 above the cutting tool 102, the cutting tool is bothcentralised and stabilised in the tubular.

Once cut, the cut section of tubular 30 can be removed, if desired, byknown means which may include unsetting and resetting the anchormechanism 110 at a top of the tubular 30 to be used as a spear, to leavethe tubular stub 109 in the well 107.

Referring now to FIGS. 9 and 10 of the drawings there is illustrates aportion of an anchor mechanism, generally indicated by reference numeral210, according to an embodiment of the present invention. Like parts tothose of FIGS. 1 and 2 have been given the same reference numeral withthe addition of 100.

Anchor mechanism 210 is formed as for anchor mechanism 110, with theaddition of a locking arrangement 21. The second cylindrical body 160with the machined cone 216 is shown with a single piston housing 168having a piston rod 176 arranged to act on a slip 212. As for theearlier embodiments there will be a number of piston housings arrangedequidistantly around the unitary body 60.

Each piston housing 168 is a cylindrical bore 174 containing the pistonrod 176. In this arrangement the back plate 178 is now placed around thepiston rod 176 so that the spring 222 is now located behind the plate178 and acts on the back face 180 biased against a wall 23 23 of thepiston housing 168 beside the port 228. In this way the piston rod 176is now biased out of the housing 168 and moving the slip 212 up the cone216. Movement of the piston rod 176 is prevented by the lockingarrangement 21. The end cap 70 is now replaced by a housing 25 throughwhich is arranged a collet support 27 connected to an end of thesecondary piston 44 with a collet ring 31 located around the support 27.Fixed in the housing 25 is the collet 33 comprising eight dogs 35 a-h,shown in FIG. 10, which engage the collet ring 31. As illustrated inFIG. 9, the collet 33 prevents movement of the piston rod 176 untilsufficient fluid force is placed on the back face 180 of the piston rod176 via the port 228, to cause the dogs 35 a-h to pass over the colletring 31. The spring 222 then biases the slips 212 in the extendedconfiguration and can be used to raise cut sections of tubular. To resetthe locking arrangement 21, the emergency release system 142 is operatedas described herein before with the dogs 35 a-h now moving back over thecollet ring 31 and the collet 33 being placed in the initialconfiguration. As for the earlier embodiments, this is preferably donehydraulically by use of a drop ball to block port 128 and direct fluidinto the port 143. However it can be achieved at surface by use of abolt 37 attached to the collet support 27, arranged through the end cap39 of the housing 25.

The principle advantage of the present invention is that it providesapparatus and method for anchoring a string at a well for the purpose ofcutting a tubular in which the anchor mechanism has independentlyactivated slips.

A further advantage of an embodiment of the present invention is that itprovides apparatus and method for anchoring a string at a well for thepurpose of cutting a tubular in which the anchor mechanism has asecondary release mechanism with active slip retraction.

A yet further advantage of an embodiment of the present invention isthat it provides apparatus and method for anchoring a string at a wellfor the purpose of cutting a tubular in which a combination of slips andstabilisers are used to centralise the apparatus and cutting tool in thetubular with the stabilisers going to drift and the slips then grippingthe tubular.

It will be apparent to those skilled in the art that modifications maybe made to the invention herein described without departing from thescope thereof. For example, while fluid pressure pistons are used tomove the slips, the pistons may be actuated by alternative means such asmechanical or electrical. Also, while the terms ‘upper’ and ‘lower’ havebeen used these are relative and the invention finds use in deviated orhorizontal wellbores. The string is referred to as a drill string but itwill be appreciated that any string of tubular pipe may be used. Whilethe method is described with reference to cutting the outermost tubulari.e. the conductor, the apparatus finds application in cutting a sectionof tubular of any diameter in a wellbore.

1. Apparatus for anchoring a string at a well for the purpose of cuttinga tubular, including an anchor mechanism, the anchor mechanismcomprising: a tubular body having a central bore between a first inletand a first outlet, the first inlet and first outlet being adapted forconnection in a drill string to be run into the tubular; a cone arrangedaround the tubular body, the cone having an outer surface including aslope; a plurality of selectively operable slips, each slip having anouter surface configured to grip an inner surface of the tubular and aninner surface matching the slope of the cone they are arranged upon; anda plurality of pistons, there being a piston for each slip, each pistonbeing operable to act to move each slip independently over the conebetween a retracted configuration and an extended configuration whereinthe outer surface of each of the slips contacts the inner surface of thetubular.
 2. Apparatus according to claim 1 wherein the tubular body isrotatable relative to the cone.
 3. Apparatus according to claim 1wherein each piston comprises a piston rod contained within a cylinderarranged co-linearly with a central axis of the apparatus and eachpiston rod is arranged to act on a face of each slip.
 4. Apparatusaccording to claim 1 wherein the pistons are hydraulically operated byaction of fluid from the central bore.
 5. Apparatus according to claim 1wherein each piston includes an emergency release arrangement so as toensure retraction of each slip when the apparatus is moved back from theextended configuration to the retracted configuration.
 6. Apparatusaccording to claim 5 wherein the arrangement comprises a release pistonconfigured to act on each piston rod.
 7. Apparatus according to claim 6wherein the release piston is hydraulically operated by action of fluidfrom the central bore.
 8. Apparatus according to claim 1 wherein theapparatus includes a plurality of selectively operable centralisationpads, each pad having an outer surface configured to match an innersurface of the tubular and an inner surface matching the slope of thecone they are arranged upon; and the plurality of pistons including apiston for each centralisation pad, each piston associated with acentralisation pad being operable to move each centralisation padindependently over the cone between a retracted configuration and anextended configuration wherein the outer surface of each of thecentralisation pads is at drift to the inner surface of tubular. 9.Apparatus according to claim 8 wherein the slope of the cone at eachcentralisation pad is steeper in gradient than the slope of the cone ateach slip.
 10. Apparatus according to claim 8 wherein there are an equalnumber of slips to centralisation pads on the apparatus and acentralisation pad is located between each slip and spaced equidistantlyaround a circumference of the tool body.
 11. A method for anchoring astring at a well and cutting a tubular, comprising the steps: (a)mounting apparatus on a drill string, the apparatus including an anchormechanism, the anchor mechanism comprising: a tubular body having acentral bore between a first inlet and a first outlet, the first inletand first outlet being adapted for connection in a drill string to berun into the tubular; a cone arranged around the tubular body, the conehaving an outer surface including a slope; a plurality of selectivelyoperable slips, each slip having an outer surface configured to grip aninner surface of the tubular and an inner surface matching the slope ofthe cone they are arranged upon; and a plurality of pistons, there beinga piston for each slip, each piston being operable to act to move eachslip independently over the cone between a retracted configuration andan extended configuration wherein the outer surface of each of the slipscontacts the inner surface of the tubular; (b) mounting a cutting toolon the drill string; (c) running the drill string in the wellbore andlocating the cutting tool at a location at which the tubular is to becut; (d) setting the slips independently to anchor the apparatus to aninner surface of the tubular to be cut; (e) cutting the tubular usingthe cutting tool; and (f) unsetting the slips to release the apparatusfrom the inner surface of the cut section of tubular.
 12. A methodaccording to claim 11 wherein the method includes the step ofhydraulically actuating the pistons to contact the slips to the innersurface of the tubular.
 13. A method according to claim 11 wherein themethod includes the step of applying an over pull to the anchormechanism once the slips have contacted the inner surface of thetubular.
 14. A method according to claim 11 wherein the step ofunsetting the slips is by applying a downward force to the tool.
 15. Amethod according to claim 11 wherein the cutting tool is operated viarotation of the drill string with the anchor mechanism set against thetubular to provide stability to the cutting tool.
 16. A method accordingto claim 11 wherein the method includes radially extending centralisingpads independently on the anchor mechanism.
 17. A method according toclaim 11 wherein the method includes activating an emergency releasearrangement to unset the anchor mechanism and draw the slips away s fromthe inner surface of the tubular in the event that they don't release.18. A method according to claim 11 wherein the cut section of tubing isremoved from the well by using the anchor mechanism as a spear.